Minimum power

1. asi123

258
1. The problem statement, all variables and given/known data

Hey, guys.
I have this guy trying to lift this cylinder pass the step with minimum force and so is the question, what's the minimum power that he needs to use and at what angle (alpha)?
The thing I don't understand is, why when the momentum of the weight and the momentum of the force equal one to another, you can say that the force is minimum? I mean, I can understand that there's no angular acceleration, but why is it minimum (the force)?
10x.

2. Relevant equations

3. The attempt at a solution

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Staff: Mentor

You mean (I presume) moment (or torque) not momentum. The torque due to the weight is what the man must overcome to lift the cylinder over the step. So the minimum torque that he must exert is equal to the torque due to the weight. Of course, he'd choose an appropriate angle to use the minimum force to produce that torque.

258
Thanks.